Viscometers



Nov. 6, 1962 MCKENNELL ETAL 3,062,040

VISCOMETERS' Filed 001;. 27. 1959 PULSE GENERATOR H6:

FIG 3 TIMING OSCILLATOR CIRCUIT TRANSFORMER PRIMARY sou-mom COIL 9 ,vlscomETER PROBE I nventor: RAYMOND MCKENNELL GEOFFREY BRADFIELD United States Patent Ofiice 3,062,040 Patented Nov. 6, 1962 3,062,040 VISCOMETERS Raymond McKennell, Sale, and Geoffrey Bradfield, Surbiton, Surrey, England, assignors to Ferranti Limited, Hollinwood, England, a company of Great Britain and Northern Ireland Filed Oct. 27, 1959, Ser. No. 849,028 Claims priority, application Great Britain Oct. 31, 1958 Claims. (Cl. 73-59) This invention relates to viscometers of the kind having a vibrating element for immersion in a fluid, the damping of the vibrations caused by the fluid being measured to give an indication of the viscosity of the fluid.

In order to determine a value for viscosity in this manner it is necessary that the waves generated in the fluid should be restricted to a tangential shear mode, and complete attenuation of the wave normally occurs within a distance of the order of 0.001 inch from the surface of the vibrating element. Consequently, any contamination of the element by crystallisation of the fluid or by deposits of sediment or sludge, for example, will seriously impair the measurement. In some applications, therefore, it is often necessary to remove the element for cleaning and in an industrial process plant this is a serious disadvantage.

A further disadvantage is that the element may have to be removed to be cleaned each time the fluid is changed and in some industrial batch processes this is a frequent occurrence.

It is an object of the present invention to provide a viscometer of the above-mentioned kind in which these disadvantages are obviated.

According to the present invention a viscometer of the kind having an element adapted for whole or partial immersion in a fluid and having means for imparting torsional or longitudinal vibrations to said element for producing shearing stresses in said fluid is provided with means for causing either additional or alternative vibrations of said element whilst said element is immersed in said fluid, said additional or alternative vibrations being of such an amplitude that any matter adhering to the surface of said element is removed.

In cases where the matter adhering to the surface of said element is particularly tenacious, said additional or alternative vibrations may be of an amplitude suflicient to cause cavitation of the fluid in the vicinity of the surface of said element.

If the vibrations of said element are in a torsional mode it is necessary that the additional or alternative vibrations are in a longitudinal mode if cavitation of the fluid is desired.

Said additional or alternative vibrations may be applied periodically by means of a mechanical or electronic timer.

One embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a sectional elevation of the operative parts of a viscometer,

FIGURE 2 is a sectional elevation of a modified form of the viscometer shown in FIGURE 1, and

FIGURE 3 is a block diagram of a timing mechanism suitable for use with the viscometer of FIGURE 2.

Referring now to the drawings a viscometer includes a composite tubular element comprising a nickel-alloy tube 1 having interposed along its length a tubular portion 2 of magnetostrictive material. The magnetostrictive portion 2 is subjected to an axial magnetic field provided by a permanent magnet assembly 3 and also to a tangential magnetic field perpendicular to the axial magnetic field and provided by diametrically opposite closed loop secondary windings 4 and 5 of a transformer 6. The

primary winding (not shown) of the transformer 6 is provided with a pulsed input, each pulse induced in the secondary windings 4 and 5 causing the magnetostrictive portion 2 to be subjected to crossed magnetic fields which thus cause vibrations of the composite tubular member at its resonant frequency in a torsional mode.

The permanent magnet assembly 3 and the transformer 6 are enclosed in a casing comprising a base member 7 and a cylindrical portion 8. The base member 7 is rigidly secured to the nickel-alloy tube 1 at a nodal point to ensure minimum loss of energy from the tube 1 when it is vibrating.

In operation the part of the tube 1 projecting from the base member 7 is wholly immersed in a fluid the viscosity of which it is desired to measure. The fluid causes damping of the amplitude of the vibrations in the tube 1 and the pulse repetition frequency of the input to the primary winding of the transformer 6 is so chosen that in the time interval between pulses the amplitude of the vibrations of the tube 1 decreases from a first predetermined value to a second predetermined value due to the damping caused by the fluid. The length of time taken for this decrease in amplitude to occur is measured to give an indication of the viscosity of the fluid.

In order to cause additional vibrations of the tube 1 of larger amplitude than the greatest amplitude of the torsional vibrations an electronic oscillator (not shown) is provided which generates a train of pulses of suitable amplitude and repetition frequency. The output of the oscillator is periodically applied to the primary winding of the transformer 6, the periodicity and duration being controlled by an electronic timer (not shown) according to the fluid in which the tube 1 is immersed. Vibrations of larger amplitude than the greatest amplitude of the torsional vibrations are thus caused in the tube 1 whilst it is still immersed in the fluid whereby any matter adhering to the surface thereof is removed.

In cases where any matter deposited on the probe is particularly tenacious it is preferred to cause additional or alternative vibrations of an amplitude large enough to cause cavitation of the fluid in the vicinity of the probe since this has a much greater scouring effect on the surface of the probe.

To achieve local cavitation of the fluid the modified form of viscometer shown in FIGURE 2 of the drawings is preferred. The viscometer shown in FIGURE 2 is similar to that shown in FIGURE 1 and like parts have been given the same reference numerals. The viscometer is modified by providing around the magnetostrictive portion 2 a coaxial solenoid coil 9 to which is periodically applied for short periods, by a suitable timing mechanism such as that diagrammatically illustrated in FIGURE 3, the output of an electronic oscillator having a frequency the same as the natural resonant frequency of the composite tubular member in a longitudinal mode, thus causing alternative vibrations of the composite tubular member in a longitudinal mode, the normal input to the primary winding of the transformer 6 being disconnected during the periods in which these alternative vibrations are applied.

The amplitude of the output of the oscillator is made sufficiently large to cause alternative vibrations of the composite tubular member in the longitudinal mode of suflicient amplitude to cause local cavitation of the fluid in the vicinity of the tube 1, thus producing a greater scouring effect and making the viscometer particularly suitable for use in a liquid which is likely to deposit particularly tenacious material on the surface of the probe.

In viscometers in which the vibrations imparted to the element are in the longitudinal mode additional vibrations may be applied to the element of suificient amplitude to cause local cavitation of the fluid without any necessity of changing the mode of vibration.

It will be appreciated that the invention is applicable to viscometers in which the vibrating element is driven by means other than that described above, for example, the invention is applicable to viscometers having electromagnetic, electrostatic or piezoelectric driving means.

What we claim is:

1. A viscometer comprising a vibratory element adapted for at least partial immersion in a fluid, means for causing said elements to vibrate in one of the torsional and longitudinal modes to produce shearing stresses in said fluid, and means for producing other vibrations in said element whilst said element is immersed in said fluid, said other vibrations having an amplitude suflicient to remove from the immersed surface of said element any matter adhering to said surface.

2. A viscometer as claimed in claim 1 wherein the amplitude of said other vibrations is suflicient to cause cavitation of the fluid in the vicinity of the immersed surface of said element.

3. A viscometer as claimed in claim 1 including a timing mechanism for producing said other vibrations in said element periodically.

4. A viscometer comprising an element adapted for at least partial immersion in a fluid, means for causing said element to vibrate in the torsional mode to produce shearing stresses in said fluid, and means for producing additional vibrations in said element whilst said element is immersed in said fluid and is vibrating in the torsional mode, said additional vibrations being in the longitudinal mode and having an amplitude suflicient to remove from the immersed surface of said element any matter adhering to said surface.

5. A viscometer comprising an element adapted for at least partial immersion in a fluid, means for causing said element to vibrate in the longitudinal mode to produce shearing stresses in said fluid, and means for producing alternative vibrations in said element whilst said element is immersed in said fluid, said alternative vibrations also being in the longitudinal mode and having an amplitude sufiicient to cause cavitation of the fluid in the vicinity of the immersed surface of said element and thereby remove from said surface any matter adhering thereto.

References Cited in the file of this patent UNITED STATES PATENTS 2,514,080 Mason July 4, 1950 2,839,915 Roth et a1 June 24, 1958 2,860,646 Zucker Nov. 18, 1958 2,896,648 Lazarus July 28, 1959 OTHER REFERENCES A New Method for Continuous Viscosity Measurement. General Theory of the Ultra-Viscoson, Roth and Rich, Journal of Applied Physics, volume 24, number 7, July 1953. 

